(a) Field of the Invention
The present invention relates to a method for manufacturing an ultrasonic transducer for an ultrasonic probe device used as medical equipment.
(b) Description of the Prior Art
A piezoelectric ceramic is conventionally used for a piezoelectric resonator as an ultrasonic transducer in an ultrasonic probe. Such a piezoelectric ceramic is divided into ring-, dice- or array-shaped elements in accordance with an intended application of the resultant transducer. In order to obtain array-shaped elements from a piezoelectric ceramic, electrodes are connected to two ends of a piezoelectric ceramic by FPC (flexible printed circuit) plates or the like. Thereafter, a backing material (e.g., a rubber) as a noise absorbent is adhered to the piezoelectric ceramic through the FPC plate. Then, the piezoelectric ceramic is divided into strips of a predetermined size using the backing material as a support.
However, if ring- or dice-shaped elements are desired, it is impossible to connect electrodes or ground terminals from two ends of the piezoelectric ceramic in view of the divided state of the ceramic. For this reason, when electrodes must be connected to the piezoelectric ceramic, lead wires must be inserted to extend through the backing material. Thereafter, the piezoelectric ceramic and the backing material are adhered together, and the assembly must be cut into a predetermined concentric or lattice format with a laser beam. When such a process for manufacturing a transducer is adopted, manufacturing presents difficulties in respect of a positioning precision of lead wires or the like. Furthermore, the processing with the laser beam adversely affects the cut surface of the backing material (generally a rubber) which has a low thermal conductivity. The heat resistance of the adhesive for the backing material must also be considered.
When a ground terminal is to be connected, a method as shown in FIG. 1 has been proposed if a divided piezoelectric ceramic is disc-shaped. According to this method, referring to FIG. 1, a disc-shaped ceramic 2 divided into concentric elements 2a, 2b, 2c and 2d is fixed on a backing material 1. A thin copper foil 3 is soldered across the elements 2a, 2b, 2c and 2d. Ground lead wires are connected to the copper foil 3. In FIG. 1, reference numeral 4 denotes lead wires.
When ground lead wires are connected according to this method, the copper foil on the upper surface of the piezoelectric ceramic causes undesired oscillation to adversely affect the acoustic characteristics of ultrasonic waves generated by the piezoelectric ceramic. When a preformed coating material is adhered on the upper surface of the piezoelectric ceramic to form a matching layer in order to improve acoustic characteristics, the adhesion surface becomes nonuniform due to the soldered copper foil, resulting in defective adhesion. When a coating material of an epoxy resin is coated on the upper surface of the piezoelectric ceramic to form a matching layer, the coating layer will have a uniform thickness upon polishing. However, upon such polishing, the copper foil may be exposed to the surface or become separated, which is not preferable from the viewpoint of safety.